The present invention relates to a sheet material feeding apparatus that intermittently feeds a sheet material a predetermined quantity by a predetermined quantity to a work machine such as a press apparatus, etc., and more particularly, to a sheet material feeding apparatus suited to feeding of a thin sheet material.
A new technology, such as development of hybrid cars in auto industry, etc., associated with the global environmental problem and products employing the technology are actively developed in respective industries. The hybrid technology of automobiles is based on the combination of an engine and a motor and one of themes of the technology resides in developing a further efficient motor. While motor cores used in such motors are manufactured by laminating thin sheets, which are punched by a press apparatus, in several layers, it has been found that with a view to an improvement in efficiency, it is preferable to make thin sheets, which are laminated, further thin.
In such situation, there is a tendency that a sheet material for motor cores punched by a press apparatus becomes thin yearly, and by way of example, a silicon steel plate having a thickness of 0.25 mm is used in recent years in place of a silicon steel plate having a thickness of 0.5 mm and used before. Accordingly, press apparatuses conformed to such situation have been studied and so sheet material feeding apparatuses that feed a sheet material to a press apparatus are demanded of development that suits the apparatuses to feeding of a thin sheet material.
Conventionally, a roll feed apparatus, in which a pair of rolls interpose and convey a material, is known as a sheet material feeding apparatus.
Some roll feed apparatuses are of a type comprising a main roll continuously and rotationally driven by a drive device and a sub-roll driven by the main roll through a sheet material (see, for example, U.S. Pat. No. 5,720,421).
Also, some roll feed apparatuses are of a type, in which sector-shaped rolls are used as a pair of rolls and a material is conveyed by swinging and rotationally driving the rolls (see, for example, JP-U-63-170039).
Also, there is known a sheet material feeding apparatus comprising sheet material guide means that guides a sheet material to restrict flexure of the sheet material at the time of sheet material feeding and using the sheet material guide means to guide the sheet material upstream and downstream of a pair of rolls as viewed in a sheet-material conveyance direction (see, for example, JP-U-63-170039).
Since the sheet material feeding apparatus described above intermittently feeds a sheet material to a work machine such as a press apparatus, etc. while repeating stoppage and feeding, flexure of the sheet material is liable to generate in the intermediate of a path, along which the sheet material is fed to the work machine. Also, since a pair of rolls interpose therebetween the sheet material with a sufficient interposing force to feed the same with a friction force, the sheet material in case of a thin sheet is liable to readily wind round a roll. Such flexure of and winding of the sheet material round a roll leads to degradation in accuracy for a feeding length by the sheet material feeding apparatus to be responsible for a hindrance to the work by the work machine.
In the related art described in the JP-U-63-170039, the sheet material guide means performs guidance upstream and downstream of the pair of rolls as viewed in the sheet-material conveyance direction to restrict flexure of the sheet material but it is difficult to prevent flexure of and winding of the sheet material round a roll since a wide space is provided between the sheet material guide means and the rolls.